Pitman goes on to list several reasons to support his assertion:
It's important for local SEO; it is expected from consumers; it's necessary for link building; website content improves relevance and links; websites are essential for brand building; finally, and most importantly, websites are an important tool for customer service.
That last point is the point. As I have already mentioned twice in this post, some trends, despite their rise in popularity, neglect that which keeps customers as customers and not just curious searchers treating your Google My Business listing like they're digitally window-shopping.
In other words, if they're looking for hours, contact information, etc., and they only see a Google My Business listing, they're not likely to trust the information they provide — or, at the very least, they suspect the information listed is inaccurate.
And there's plenty of reason why it might not be, including competitors or spammers in general editing/changing your listing on Google My Business.
Treating your website like a home base means customers won't be confused on how to best reach you. You can direct them to you — well, directly — through your website.
Moreover, customers trust (your) website's accuracy: hours, contact information, phone number, location, etc. Aside from your product, this is what your customer is looking for, what they need to know. This type of information can get botched when listed on Google My Business, whereas, on your website, it's your digital storefront; it is yours. It follows logically, then, why a consumer would trust you more than your listing: the assumption is that, if it's your website, the information listed would be the most accurate.
This brings us to another important point: your website itself. Given the importance of a website, despite the GMB trend, your website itself needs to be strong, clean, easy to navigate, not have long load-times — in short, it needs to look, feel and be professional in order for the customer to think of you professionally.
This itself strengthens the importance of working with a professional digital advertising agency. They know what consumers want when it comes to websites, and, moreover, they know how to build a website that delivers.